G'day arti, the English word "lockdown" in the Coronavirus context has a clear meaning which "uzamčení" (closure, locking, locking away, locking up) doesn't, so the word "lockdown" is now used (and declined*) quite normally in the Czech media. Very occasionally (i.e. rarely**), I've seen "lokdaun" probably more as a pronunciation guide, but it hasn't caught on - neujalo se.
There's even an article about it Slovem roku je "lockdown", píše prestižní slovník on aktualne.cz here. Interestingly, this article uses "uzávěra či plošná karanténa" to describe the meaning of the term, and not "uzamčení".
* V Německu to vypadá na Vánoce s lockdownem (source: ihned.cz); Celkovou snahou podle něj je, aby společnost nežila od lockdownu k lockdownu a opatření se neměnila ode zdi ke zdi. (ceskatelevize.cz) etc.
** To půjdeme od "lokdaunu" k "lokdaunu"? So we're going to go from one lockdown to the next? [Note this was written by Joe Public in the comments section, not by a card-carrying member of the journalistic game profession.]